Cap 15

of 
 paraxonemal bodies in Tetrahymena paravorax and 
Glaucoma ferox , two ciliates that are predatory, 
and sometimes cannibalistic . Perhaps, the develop-
ment of these paraxonemal bodies increases the 
capture efficiency of these predators. 
 The oral cavity of hymenostomes , and particularly 
its organization and development in Tetrahymena , 
has been the subject of both extensive and intensive 
investigations (Forer, Nilsson, & Zeuthen, 1970; 
Frankel, 1991; Frankel, Jenkins, Bakowska, & 
Nelsen, 1984a; Frankel, Nelsen, Bakowska, & Jenkins,
1984b; Nilsson, 1976; Williams & Bakowska, 
1982). The oral polykinetids of hymenostomes are 
characterized as membranelles . The membranelle 
is typically oriented transversely in the oral cavity, 
has postciliary microtubular ribbons associated 
with the right-most row of kinetosomes, has no 
alveoli between the rows, and has parasomal sacs 
distributed irregularly between the kinetosomes. 
 Membranelles have been characterized as being 
linked within by distal and proximal filamentous 
systems and between by a proximal filamentous 
system (Grain, 1984; Grain & de Puytorac, 1976). 
This structure has been observed in Tetrahymena
(Nilsson, 1976), Glaucoma (Peck, 1978), and 
Colpidium (Lynn & Didier, 1978). Nevertheless, 
Peck (1977a, 1978) makes a reasonable argument 
against this view, suggesting that there is consider-
able variation. A case in point is the hymenostome 
Turaniella , a predator on other ciliates. Its oral 
cavity is much-expanded and its oral polykinetids 
and underlying filamentous systems are extremely 
well-developed, bearing some resemblance to the 
 peniculines with which it was formerly associated 
(Iftode & Grain, 1975; Iftode, Versavel, & Didier, 
1970). However, the ultrastructure of its somatic 
cortex and its stomatogenesis demonstrated clear 
affinities to the hymenostomes with which it is now 
15.4 Oral Structures 311
312 15. Subphylum 2. INTRAMACRONUCLEATA: Class 9. OLIGOHYMENOPHOREA
classified (Didier, Iftode, & Versavel, 1970; Iftode 
et al., 1984). It is very likely, therefore, that the 
complicated fibrillar systems of the oral structures 
of Turaniella have converged on the peniculine 
model, correlated with the predatory feeding pref-
erence of this macrostomatous hymenostome . 
 Functioning of the hymenostome oral apparatus 
has been elucidated by studies on other macros-
tomatous hymenostomes , Tetrahymena vorax and 
Tetrahymena paravorax . The macrostome forms 
of these species have an expanded oral region 
with a large cytopharyngeal pouch in which to 
capture ciliate prey. The oral apparatus is modi-
fied, through morphogenesis , from that of the 
 microstome form by increasing the number and 
arrangement of kinetosomes in the paroral and 
oral polykinetids (Smith, 1982). Food vacuoles 
appear to be formed by a contractile mechanism 
that involves the microtubules of the ribbed wall, 
which extends from near the kinetosomes of the 
paroral, and contractile proteins around the cyto-
stome (McLaughlin & Buhse, 2004; Méténier, 
1984b; Smith-Somerville & Buhse, 1984). The 
disruption of food vacuole formation by actin 
antagonists, such as cytochalasin and latrunculin B , 
implicates this filamentous protein in the process 
(Grønlien et al., 2002; Zackroff & Hufnagel, 2002). 
Exploitation of genetic constructs in Tetrahymena
has now corroborated the important role of actin 
in food vacuole formation (Williams et al., 2006) 
and, in association with myosin , in the movement 
of food vacuoles through the cytoplasm (Hosein, 
Williams, & Gavin, 2005). The ribbed wall micro-
tubules of the microstomatous Tetrahymena spe-
cies have also been implicated in feeding (Sattler & 
Staehelin, 1979). Once the phagosome is formed, 
digestion occurs in a process very similar to that 
of Paramecium , except that acidosomes are not 
involved (Nilsson, 1976, 1979, 1987). As has been 
reported from Paramecium , membrane retrieval 
and recycling likely occurs from both the early 
 phagosome during its condensation stage and after 
its fusion with the cytoproct (Mislan & Smith-
Somerville, 1986). 
 The peritrichs , as their name suggests, are char-
acterized by having ciliary structures around the 
perimeter of the peristome (Fig. 15.3). Two oral 
structures are involved – the paroral , tradition-
ally called the haplokinety , and oral polykinetid 1, 
traditionally called a polykinety . These two 
structures circle the peristome in a counter-clock-
wise direction, if viewed from the top, up to five 
times in some Campanella species. They then 
plunge into the oral cavity, traditionally called the 
 infundibulum . The peritrich oral polykinetid 1 is 
composed of three rows, parallels the paroral in its 
counter-clockwise course into the infundibulum , 
and terminates near oral polykinetids 2 and 3, 
which lie deeper in the infundibulum . Similar to 
other oligohymenophorean oral polykinetids , there 
are postciliary ribbons associated with the kineto-
somes of the rightmost row, sometimes only visible 
during stomatogenesis (Bradbury, 1965; Eperon 
& Grain, 1983; Maslin-Leny & Bohatier, 1984). 
Alveoli are absent between the polykinetidal cilia, 
parasomal sacs may be distributed between the 
kinetosomes, and a complex set of fibres and fila-
ments links the kinetosomes to each other and to a 
filamentous reticulum bordering the leftmost row. 
These features have been observed in Opisthonecta
(Bradbury), Trichodina (Hausmann & Hausmann, 
1981a; Maslin-Leny & Bohatier), Thuricola (Eperon 
& Grain), Tripartiella (Maslin-Leny & Bohatier), 
and Astylozoon (Guinea, Gil, Serrano, & Sola, 1990). 
There has been much speculation about these diver-
gent filamentous structures compared to those of the 
 oral polykinetids of other oligohymenophoreans . It 
is most likely that they are correlated with the highly 
contractile ability of peritrichs , which can bring all 
their oral ciliature “inside” the peristome as they with-
draw from irritating stimuli. 
 The peritrichs create filtering-feeding currents 
by metachronal beating of the cilia of the paroral 
and oral polykinetid 1. This creates a “peristaltic” 
flow between the cilia that traps particles and 
forces them into the infundibulum where the par-
ticles are essentially trapped on the deeper paroral 
cilia before being directed to the food vacuole 
(Fenchel, 1980a; Sleigh & Barlow, 1976). Oral 
ribs direct particles, on the outside, to the cyto-
stome, while, on the inside, the ribbed wall micro-
tubules direct diskoidal vesicles to the cytostome 
where they fuse to form the nascent phagosome 
(Allen, 1984; McKanna, 1973b). As in other cili-
ates, excess membrane, as cup-shaped vesicles , is 
removed from the early phagosome and recycled 
to the food vacuole forming region (Goff & Stein, 
1981; McKanna). 
 The paroral , stichodyad or haplokinety is a 
typical feature of the oral apparatus of the four 
preceding classes. Stichodyad refers to the diki-
netid nature of this paroral, with the pairs of 
kinetosomes so oriented after stomatogenesis that 
they are almost perpendicular to the long axis of 
the paroral so that the postciliary ribbons of the 
more oral or inner kinetosome are “on the left” 
(Grain, 1969, 1984). Haplokinety refers to there 
being only one, the outer, of the two kinetosomes 
ciliated (Grain, 1984; de Puytorac & Grain, 1976). 
While there are variations in the nature of the links 
both that connect the kinetosomes of each dikinetid 
and that link dikinetids together in the paroral, this 
basic structure is typical of the oligohymenopho-
rean paroral . It has been reported, for example, 
in the following: the peniculines Paramecium , 
Frontonia , and Urocentrum (Didier, 1971); the 
 scuticociliates Cinetochilum , Myxophthirus , and 
Paranophrys (Didier & Wilbert, 1976; de Puytorac 
et al., 1974a; Da Silva Neto,